1. Field of the Invention
This invention relates to the field of medical devices and more particularly to guidewires for use primarily in intra vascular procedures. Guidewires made with a titanium molybdenum alloy allow for a flexible and formable tip with reduced kinking, high torque, trackability and high column strength.
2. Description of the Related Art
A major requirement for guidewires and other guiding members, whether they are solid wire or tubular members, is that they have sufficient column strength to be pushed through a passageways in a patient such as the patient's vascular system with minimal kinking or binding. However, the distal section of the guidewire must be flexible enough to avoid damaging the blood vessel or other body lumen through which it is advanced. Efforts have been made to improve both the strength and flexibility of guidewires to make them more suitable for their intended uses, but strength for pushing and flexibility for turning without damaging vascular walls tend to be diametrically opposed to one another, in that an increase in one usually involves a decrease in the other. There has been a gradual decrease in the profiles or transverse dimensions of commercially available intravascular catheters and guidewires particularly for use in coronary arteries. However, concomitant with the decrease in profile has been a loss in pushability and kink resistance.
The distal portion of the guidewires frequently have a spring or coil around a tapered, thinner and therefore softer metal core. The thinner softer core may be too thin to engage the coil and may therefore allow the coil to kink when bent.
Guidewires have been made of many different materials. The most popular materials are stainless steel and NiTi alloys such as Nitinol.
Stainless steel guidewires tend to kink. They have good pushability but are not flexible enough to easily bend inside of the vascular system. Stainless steel has good torque qualities for rotating the guidewire but tends to bind when rotated since it does not readily flex. Once the guidewire is kinked, it must be discarded and replaced with a new guidewire.
NiTi guidewires tend to be too springy, especially when negotiating a tortuous path in vessels, they do not have good pushability because want to straighten out or return to their original shape. NiTi guidewires will readily get hung up when rotated while extending around a curved path. NiTi guidewires can not be torqued as readily as stainless steel because it is springy. NiTi guidewires tend to have good shape memory. The shape memory makes it difficult for a physician to shape the tip of the guidewire with his fingers for accessing difficult to reach portions of the patient's vascular system.
The guidewires need to have distal ends that are soft for bending and turning inside of the blood vessels as they are advanced and so they will not puncture the vessel walls.
The most popular guidewires are made out of stainless steel or NiTi alloys. Both of these materials have advantages and drawbacks. A different guidewire material is required to have the desirable qualities of both without as many drawbacks to enhance the performance of guidewires.